Sound transmission



April 19, 1932. w B JONES 1,855,148

' SOUND TRANSMISSION Filed Aug. 4, 1927 means are employed in PatentedApr. 19, 1932 W. BARTLETT JONES, OF CHICAGO, ILLINOIS SOUND TRANSMISSIONApplication filed August 4, 1927. Serial No. 210,629.

The present invention relates to the interception'and the transmissionof sounds, and has particular reference to the production and theshifting of virtual sound sources.

In my copending application Ser. No. 183,414, filed April 13th, 1927, Ihave described in considerable detail means for the creating of virtualorigins of sound by use of the binaural effect. Among the apparatusdescribed there are shown various sound intercepting means and variouspresentation means. For the purpose of the above named application theintercepting or transmitting ear-locations, or in other words, arebinaurally located, that is, the two sound intercepters are so locatedthat they gather in surrounding sounds substantially as do the two earsof a human being. The corresponding right and left ear-eifects thuspicked up are transmitted elsewhere, or are phonographically recordedfor presentation at a different time or place, or both, according to thecharacter of the link between the pick-up devices and the presentationmeans.

The presentation means described in the above named application are oftwo types,

generically referred to as receivers, one, the

head phones, and two, the loud speaker. The head phones are well knownas being suitable for reproducing left and right ear-effects binaurallyintercepted. The combination of binaural interception and the use ofhead phones permits thevlistener to sense the exact direction and mutualrelations of the several sound sources transmitted.

The above-named application teaches that when a pair of head phones arereplaced by a pair of loud speakers, the same space impressions may beobtained when the listener is midway between the two speakers in such amanner that sound paths of equal length prevail from each loud speakerto the nearer ear. The application also teaches that when there ismotion from the mid-position, there is an arcuate shifting ofeachvirtual source, depending upon its actual position. The degree ofarcuate shifting is unequal for the several sources, so that there iscreated a distortion of the actual relation. Such distortion providescountless combinations of virtual sources changing considerably withchanges of the listeners position amounting to only a few inches. .Thesechanges provide a pleasing variant to the source of sound or music whichis fully within the control of the listener, and it is a greatimprovement over the fixed and monotonous single location of soundreproduced by phonograph or radio.

The primary object of the present inven- 0 tion is to provide a systemfor the transmission and reception of sound of such a character that thelistener has within his own control the power to vary through infinitecombinations the apparent sounds and possibly to isolate one or more ofthe sources from the others for the concentration of his attention uponit.

Binaurally intercepted sound has been limited to presentation by earphones. of loud speakers for the presentation of binaurally interceptedsound ermits retention of all the advantages of head phones and providesin addition the many pleasing variants above mentioned, without the dis-76 advantage of the hysical connection of the body to the receivmgmeans.

The present invention aims pick-up devices in positions outside ofbinaural relation as one place the receivers or loud speakers in asimilar extra-binaural relation.

The invention may be more readily understood from the followingdescription of the to place the the digrammatic apparatus shown in theaccompanying drawings, in whlch Fig. 1 represents two associated phoneor sound channels with head phones at the receiving end andextra-binaurally located transmitters placed before several soundsources.

Fig. 2 represents an arrangement corresponding enerally to Fig. 1, withthe head phones of ig. 1 replaced by extra-binaurally located receivers,between which a listener 1s located in mid-position.

Fig. 3. represents a receiving or audltory station similar to that ofFig. 2 with rthe listener in a position other than mid-position.

Fig. 4 shows the listener in still another locations of the 65 The use 7feature and also to 80 position for illustrating the'shifting oftheorigins with such a change of position.

More particularly, Fig.1 shows a stage or platform from which issue aplurality of 5 sounds that are intercepted by two micrographic record,as described in respectively phones at extra-binaural locations. Theeffect at each microphone is transmitted or otherwise linked to thereceiving means for presentation to a human being. The transmission orlinking hereinafter referred to contemplates any suitablecarrier orchannel for sound efiects or for sound. It may comprise a simpletelephone system, a phonomy copending or it may be a single carrierapplication Ser. No. 183,414, duplex system employing a wave, eitherconducted over a single pair of wires, or radiated through the ether.

In the drawings 10 represents a stage upon which the dots representsound sources. The source 11 and the source 12 are designated for thepurpose of discussing their relation to the'sound transmissionsystem.The transmitters are two microphones l3 and 14 with their channels 15and'16 linked by suitable means 17 to the auditory station having thereceivers provided as head phones 18 and 19, associated withthe channels15 and 16. The arrangement described is distinguished from the binauralsystems by the fact that the micro bones are separated from each otherby a distance which is greater than the distance between human ears. Theare therefore considered to be outside the binaural relation. In thepresent instance they are represented as being three feet apart and areequidistant from the source .11. However, as to source 11, and any otherequidistant source, they act as if they were in the binaural relation,for the sound paths from 11 are equal in length. Thus a person listeningat the head phones will sense the source 11 directly ahead of him.source indicated in'the drawings, for example, source 12, the two soundpaths are of different lengths and the differential length in soundpaths is too great to fall'within the limits upon which the binauralefi'ect deends, which is substantially six inches.

ach one of the sources indicated will be heard either to the right or tothe left of the listener, depending upon which microphone is nearer thesource.

nated as X, Y and'Z.

The preferred form of the invention employs loud speakers as receivingmeans so that the listener may shift the mutual relations of himself andthe loud speakers to shift the locations of the virtual origins. In Fig.2 a stage 20 has three sound sources thereon which are herein shown inalinement for no important reason. They are desig- In a parallel lineten feet away there are two microphones 21 and 22, which are shownas-being four feet apart. The source Y islocated equidistant from the ythis reason,

For every other two microphones. The sound channels a1 designated 23 and24 and these respectivel connect loudspeakers 25 and 26 to the micrcphones 21 and 22.

The parts described are drawn to scal and permit an approximategraphical meas ure of the sound paths. H represents a per son positionedmidway between the low speakers, and (1 represents the distance be tweeneach speaker and the nearer earof H The distance from the source Y tothe micro phones is represented by A in both instances From Y to H theair paths of the sound trans mitted through both channels .23 and 24 anthe same inlength, being A plus d. Accord ingly H will hear the sourceof Y directly aheadof him because each ear will hear thr same sound atthe same time. This is indicated by the arrow 27 pointing to theencircled source Y. Because of the great distance between the twomicrophones the sources of X and Z will each have differential distancesfrom themicrophones greater than the binaural limit, and each will beheard in the direction indicated by the arrows 28 and 29. It will benoted that there is one source on each side of the listener H, and thatthe source Y has been isolated from the others. When the two ears hearthe same sounds in the same phase relation, as occurs when the source isfaced directly, it is easier to concentrate the attention upon it. For Hmay better focus attention upon Y than he could if he was present beforethe stage 20. a By isolating Y from the alined .grouphe has placed X andZ as much in the background as is possible by this invention. i

Fig. 3 represents a different arrangement of the auditory station. Thetransmitting end of Fig. 2 is to be considered as the source of the twoeffects for the station of Fig. 3. Loud speakers 30 and 31 are hereshown with the listener H located away from midposition. paths from thesource X through the two transmission channels are equal, whereby toplace the virtual of H. In order to show this relation it may beconsidered that the distance from X to 21 1s 11 feet and the distancefrom X to 22 is 14 feet. H is so located with reference to the loudspeakers that from one ear to speaker 30 the distance is 4 feet and fromthe other speaker to the other ear the distance than the binaural llmit,and each will be is so located that the sound source of X directly infront heard in the direction indicated by the arrow 33.

In Fig. 4 an arrangement is shown which isolates the virtual source ofZ. Loud speakers 34 and 35 are shown and are considered as the receivingstation for the transmitting means of Fig. 2. The listener H" is sopositioned between the speakers that the tWo sound paths from source Zare equal in length. From Z to 21 the distance may be considered to be11 feet, and from Z to it is 10 feet. Accordingly, for any distance Lwhich is added to the Z21 path there must be added to the Z-22 path adistance L plus 1 foot. In Fig. 4 the added distance L is shown as 2feet between the speaker 34 and the nearer ear of H". The other car istherefore 3 feet from the speaker 35. This causes the virtual source ofZ to lie directly ahead of H" in the direction indicated by the arrow36. The natural consequence of the isolation of Z is the appearance ofthe sources of X and Y at the left of I .as indicated by the arrows 37.

In Fig. 4, it may be considered that if H" moves toward speaker 34, hewill first hear Z with the ear on that side. By such a motion he maycause the virtual'source of Z to swing (counter clockwise in Fig. 4) sothat it will also be at the left side and be indistinguishable indirection from the virtual sources of X and Y. Starting from such aposition he may move from his left to right (to position of Fig. 4)swinging Z from the left to the center. As he continues to move andapproaches mid-position Z will have passed on to the. right and Y willhave been swung out from the left following Z (Fig. 2). As motioncontinues past mid-position, Y will move around to the right to join Zand X will swing about in its turn, as illustrated in Fig. 3. As motioncontinues he will be so near the right hand speaker that X will join Yand Z at the right. He will thus have selectively paraded the sources inan are from his extreme left to his extreme right, isolating each fromthe others.

In Fig. 2 the sources X, Y, and Z have been so related to each other andto the transmitting system shown, that no two sources may at the sametime be heard binaurally by the listener between the two receivers. Inorder to secure this isolation there must be a difference in thedifferential distance of each source to the microphones. Thedifferential distances should, and they do, vary by at least thebinaural limit of about six inches. For the differential is 2.5 feet.For Y it is zero. For 2 it is 1 foot. Hence, least 'aboutsix inches, oran amount which is not less than the binaural limit.

It is of course to be understood'that possibilities and increasing ascreases. The actual the and the combinations are many the number ofsources inlocation of the sources,

X sound interceptcrs,

to the intercepters,

the distance of the microphones from the sources and from each other,relative motion of the microphones and the sources, the locations of theloud speakers relative to each other, the character and intensity ofwall reflections in a room, all bear more or less upon the resultsachieved. Nevertheless, the variants are within the control of thelistener to a sufiicient extent because of the use of loud speakers.

The greatest differential which may exist at the pick-up end is ofcourse the distance between the transmitters, such as four feet in Fig.2. In order to perceive a virtual image at the receiving end so that itappears isolated into a direct-ahead position, the same differentialdistance must obtain at the receiving end. The only possible way tosecure this in open air paths is to have the two receivers separated bya distance at least equal to that maximum.

With reference to Fig. 1, it may now be seen that when the microphonesare fixedly separated and used in combination with fhead the phones,there is no flexibility in use 0 combination. a If the sources move, orif the microphones move, some effect will be observed, but it is notwithin the control of the listener. The arrangement involving loudspeakers imparts to the separated microphones a much greater and morepractical utility than any combination using head phones. However, I donot hereby mean to exclude from the invention the combination of Fig. 1,nor any other combination or feature which is defined by the appendedclaims.

I claim: .7

1. A sound transmission system comprising in combination, twotransmitters located outside the binaural location and directedgenerally toward a plurality of separated sound sources of original anddistinctive characters, two receivers directed generally toward eachother and separated by a distance at least about six inches greater thanthe distance between the transmitters, and two independent linking meansrespectively connecting said two transmitters and said two receivers,whereby a listener between said receivers may position his ears toreceive two sounds in-a binaural phasing determining direction.

2. A sound transmission system comprising in combination, a plurality ofseparated sound sources of original and distinctive characters, twoext-ra-binaurally locate and two receivers linked said receivers beingat least about six inches further apart than the intercepters, thesources and the interc'epters being so located that the difierentialdistance of each source from the inter'cepters difiers from the similardifferential distance of every other source by an amount not less thanthe binaural limit, whereby to permit a listener to isolate the virtualposition of each source from the other sources,

3. A sound transmission system compr1s ing in combination, a pluralityof separated 5 sound sources of original and distinctive characters, twoextra-binaurally located sound intercepters, and two receivers linked tothe intercepters, said receivers being at least about six inches furtherapart than the intercepters, the sources and the intercepters being solocated that the differential distance of one of the sources from theintercepters differs from the similar difierent-ial distance of theother sources by' an amount not less than the binaural limit, whereby topermit a listener to isolate the virtual position of said one sourcefrom the virtual positions of the remaining sources.

4. A sound transmission system comprising in combination, a plurality ofseparated sound sources of original and distinctive characters, twoextra-binaurally located sound intercepters, and two receivers linked tothe intercepters, said receivers being. at least about six inchesfurther apart than the intercepters, the sources and the interceptersbeing so located that the differential distance of one of thesourcesfrom the intercepters diflers from the similar differential distance ofthe other sources by an amount which is sufliciently close to thebinaural limit topermit a substantial isolation of the virtual positionof said one source from the virtual positions of the remaining sources.5. The method of transmitting sound for binaural reception and, forseparation of the binaural images which consists of intercepting thesame sound waves from separated sources of original'and distinctivecharacters, 40 said interception taking place at two points locatedoutside the binaural location, separately reproducing the interceptedsounds, and presenting the reproduced sounds to the ears of a listenerin such a way that the two sounds reach the ears over time-delay paths,and such that one ear hears one intercepted version and the other earhears the other intercepted version, each-ear hearing its respectiveversion before it hears any other version, whereby binaurally phasedcomponents determine a binaural image, and changing the differential inthe time of delay in said paths, whereby to vary the time of arrival ofthe reproduced sounds, and to bring other a components into binauralphasing relative to the time of arrival at the ears.

In testimony whereof I hereunto aifix my signature.

W. BARTLETT JONES.

